added reference link. (#8667)

* added reference link.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: rohan472000

electronics/apparent_power.py

@@ -8,6 +8,8 @@ def apparent_power(
     """
     Calculate the apparent power in a single-phase AC circuit.
 
+    Reference: https://en.wikipedia.org/wiki/AC_power#Apparent_power
+
     >>> apparent_power(100, 5, 0, 0)
     (500+0j)
     >>> apparent_power(100, 5, 90, 0)